1. Field of the Invention
The present invention relates to a nonelectric delay initiator for transmitting an explosion from a donor low-energy detonating cord to a receiver low-energy detonating cord, and to an assembly containing said initiator for the connection of said cords and initiation of the receiver cord.
2. Description of the Prior Art
The hazards associated with the use of electrical initiation systems for detonating explosive charges in mining operations, i.e., the hazards of premature initiation by stray or extraneous electricity from such sources as lightning, static, galvanic action, stray currents, radio transmitters, and transmission lines, are well-recognized. For this reason, nonelectric initiation through the use of a suitable detonating fuse or cord more and more has been capturing the interest of blasters.
Low-energy detonating cords, usually those having an explosive core loading of up to about 2 grams per meter of cord length, are very useful detonation-transmitting means for nonelectric detonation systems because they are characterized by low brisance and the production of little noise, and therefore can be used as trunklines in cases where noise has to be kept to a minimum, and as downlines in systems in which the cord must not be so brisant as to detonate the borehole charge or an adjacent section of cord. A "trunkline" is a common surface line of detonating cord from which multiple "downlines" of detonating cord depend and extend to explosive charges emplaced in various boreholes.
An improved low-energy detonating cord (LEDC) which is light-weight, flexible, and strong, detonates at high velocity, and is readily adapted to high-speed continuous manufacturing techniques is described in U.S. Pat. No. 4,232,606, issued Nov. 11, 1980, the disclosure of which is incorporated herein by reference. This cord can be initiated reliably by means of a coaxially abutted blasting cap, but not by the detonation of another length of detonating cord with which it is spliced or knotted. A field-connected explosive booster for propagating a detonation in connected detonating cord assemblies containing a cord such as that described in the aforementioned U.S. Pat. No. 4,232,606, e.g., an explosive starter for initiating a receiver low-energy detonating cord by means of a donor low-energy detonating cord, is described in co-pending U.S. Pat. No. 4,248,152, issued Feb. 3, 1981. One cord, usually the receiver, is inserted into an axial cavity of the booster in a manner such that an end-portion of the cord is surrounded by a granular explosive, and the other cord, usually the donor, is positioned transversely outside and adjacent to a closed end of the booster shell, preferably in a transverse slot in a tube which holds the booster. Detonation of the donor cord causes the instantaneous detonation of the receiver cord.
A nonelectric delay detonator adapted for field-assembly with a cord such as that described in the aforementioned U.S. Pat. No. 4,232,606 for the purpose of actuating the detonator is described in co-pending U.S. patent application Ser. No. 177,210, which is a continuation-in-part of Application Ser. No. 015,288, filed Feb. 26, 1979, now abandoned. The cord, e.g., a downline, is inserted into a deformable expansion shell, and the pressure pulse resulting from the detonation of the cord causes the shell to expand and an ignition charge around the expansion shell to be actuated as a result of sudden compression between the expansion shell and a rigid capsule. This results in the ignition of the delay and priming charges and detonation of the base charge.
In the art of nonelectric delay blasting there is need for a surface delay device adapted for field-assembly that will end-initiate a low-energy detonating cord (receiver cord), e.g., a trunkline or downline, from the side output of a low-energy detonating cord (donor cord), e.g., trunkline, transversely positioned outside a borehole, while providing a precise delay in the initiation of the receiver cord. The nonelectric delay detonator described in the aforementioned application Ser. No. 177,210 is adapted to be actuated by an axial cord (e.g., a downline cord) only, and thus is suited for use as an in-the-hole detonator to set off a blasting charge therein, directly or via a primer. The availability of a nonelectric delay initiator which could provide a precise delay between two trunklines, or between a trunkline and downline (as a delay starter) would provide the capability of delaying the firing of borehole charges at the surface as well as in the borehole.
Other nonelectric delay initiators are known which, like the detonator of U.S. application Ser. No. 015,288, are adapted to be actuated by percussive force applied thereto by an axial detonating cord. For example, U.S. Pat. No. 3,106,892 shows a delay initiator which is actuated by the end-output of a low-energy detonating cord. This initiator contains the usual ignition-to-detonation train in a tubular shell, i.e., starting at the closed end, first a base charge of detonating explosive, then, in sequence, a priming charge, a charge of exothermic-burning delay composition, and a capsule housing a percussion-sensitive ignition composition and a spacing member, the ignition composition being positioned between the closed end of the capsule and one end of the spacing member which forms an anvil head, and the air gap provided by the spacing member extending from the ignition composition to the delay composition. A booster charge of detonating explosive abuts the closed end of the capsule, and a length of low-energy detonating cord closes the open extremity of the shell with the cord end abutting the booster charge. The end output of the cord, after being "boosted" or intensified by the booster charge, applies the necessary percussive force to the ignition capsule.
Another delay detonator actuated by the percussion produced from a detonating cord adjacent a capsule containing a percussive-sensitive ignition composition is described in U.S. Pat. No. 3,709,149. In this detonator, as in the detonator described in U.S. Pat. No. 3,106,892, a spacing member provides an air gap between the percussion-sensitive ignition composition and the delay composition. Furthermore, in the detonator assembly shown in U.S. Pat. No. 3,709,149 any receiver detonating cord which may be present (e.g., downline 9 as a receiver cord with respect to detonator assembly 6') is positioned outside the detonator shell.
U.S. Pat. No. 3,776,135 also describes a cord-actuated delay detonator, the cord in this case being separated from the ignition charge by a perforation to allow venting of gases.
U.S. Pat. No. 3,205,818 does not describe a detonator, but it shows a connector for securing two detonating cords in perpendicular, operative relationship to one another. A capsule containing a booster charge of high-velocity detonating explosive is crimped to one end of a length of LEDC which abuts the booster charge. The bottom, closed end of the capsule is positioned adjacent to the side of a length of detonating fuse in a transverse slot in a tube which holds the capsule/LEDC assembly.
In summary, none of the cord-actuated delay initiators known to the art are adapted to be ignited from the side output of a transversely positioned cord to bring about the detonation of an axial cord. Although the detonator described in the aforementioned U.S. Pat. No. 3,709,149 is adapted to be ignited from the side output of a cord transversely positioned outside the detonator capsule, the ignition-to-detonation train progresses in the direction of the base of the detonator capsule, and no provision is made to affix an axial detonating cord thereto for the detonation thereof.
A detonator having an ignition-to-detonation train in a reversed direction is described in U.S. Pat. No. 2,652,775, but this detonator is not a delay detonator and no detonating cords are used therewith. The detonator, which is designed for firing a blasting charge in a well, comprises a tubular metal shell containing a thin layer of an impact-sensitive ignition charge pressed against a flat, thin closed end thereof, a metal anvil interposed between the ignition charge and an explosive priming charge, and a pressed main detonator charge adjacent to the priming charge. The anvil is either of slightly smaller diameter than the inside of the shell, or is provided with channels or perforations. A sealing plug closes the other end of the shell. To actuate this detonator, the ignition end of the shell is depressed by a firing pin moved by the impact of a dropping weight and a striker rod. The ignition charge is thereby squeezed between the shell and the anvil, and ignited. The resulting flash is transmitted to the priming charge, and the main charge detonates, thereby setting off a surrounding blasting charge.